Electrolytically generated oxygen for caustic recovery



ELECTROLYTICALLY GENERATED OXYGEN FOR cAUsTIC RECOVERY Nev. 4, 1958 c. w. RIPPIE ET AL 2r sheets-sheet 1 Filed Dec.

.n .rm L' Nav. 4, 1958 c. w. RlPPlE ET AL ELECTROLYTICALLY GENERATED OXYGEN FOR CAUSTIC RECOVERY 2 Sheets-Sheet 2 Filed Dec.

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United States 'Patent ELEC'rRoLYrIcALLY GENERATED YOXYGEN FoR-cAUsrlc RECOVERY Charles W. Rippie, Ashland, Ky., IandHoward B. Bishop,

Summit, N. J., assignors Vto H. Berkey Bishop, Morristown, N. J. v

This invention relates `to theoxidation of mercaptides to disuldes in aqueous-alkaline reacting solutionsand to other reactions which require oxidation.

In the'rening of -petroleum oils to eliminate some of the chemical components which detractzfrom ,the value of the oil and particularly in thedesulfurization ofgasoline large quantities of caustic solutionsA arenormally employed. l v A T he usual lprocedure is .to treatithev gasoline first to relmove hydrogen sulfide, then caustic soda or. other alkaline .hydroxides are, used for vthe extractionV of mercaptans. Several methods have' hitherto beeniemployedfor the'regeneration' of the hydroxides Lincludingitheffollow'- fing: ,I y

(l) One method. isto adddoetorzsolution l which consistsvrof sodium plumbite, Which,;combined withtfreesulfur, ,results in the oxidation Y of rlmercaptides .and .other sulfurfhydrolV compounds to innocuouszdisulides and i the .precipitation ofthelead as leadsulde. This procedure involves the Vregenerationof vthe spent doctor :solution by. oxidation for the recovery of leadJslflde.

(-2) Another d,method oil-'regenerating the hydroxidesfis fto utilize theisolution containing `the aqueous-mercaptides as an electrolyte and pump thezsolution-throughoneor .moreelectrolyticicells where the waterisbroken-,down and oxygen produced-whichlcombines Withtheialkaline vmercaptides and formsdisultde. Y

The rst processtutilizing the doctor solution hasth disadvantage of leaving thel disuldes in-.the gasoline `and .requiringtheregeneration of the spent doctor,

The secondgprocess, which-isgenerally known easthe internal electrolytic regeneration process, Yhas the disadvantage'thattthe caustic solution employed in the treatl' ing process must be such as Ytoconstitute a favorable electrolyte in the electrolytic cell and therefore the selec- .tio-ny of the .caustic treatingsolution isin themature :of a

compromise between theconditions desired vfor treating Y the gasoline and the conditions necessaryto maintain the solution and provides no means Vfor eiectively mixing the oxygen produced with the solution. Also the electrolytic cell is subject to rapid deterioration becausecorrosive substances are formed inside the cell.

This invention has for its purpose the utilization of an electrolytic cellwith an ideal electrolyte for the produc- 'tionof oxygen Vand-the-'ellicient use-of the oxygen outside ofthe cellffor-the regeneration ofy the spentl caustic. It is thus possible to utilize-the most economicalandsatisfactory caustic solution for thetreatment ofggasoline without reference to Whether or not Vit would be -af satis- 'factory electrolyte. Y

ItHhas beenfound to'be entirely feasible to'employ ahigh cost caustic such as` causticpotash inside the; cell, since it will not wearout for -a long period` of` time, such as'iveyea.rs,-and is more `desirable-andsatisfactoryaas an ice . 2 electrolyte for use in .the cell. At the same `time it is entirely feasible Ato employ a low cost caustic, such Aas caustic soda, for'trea'ting lthe gasoline lsince it does not enterthe cell. and is not `relied upon `as anelectrolytel A rOther satisfactory electrolytes, such as acid, may be employed Vs'inceztlie oxygen produced lin the cell isto be used outside of the cell.

This invention takes advantage of the fact, we `have discovered, that the oxygen gen'eratedin the elec- .trolytic .cell is a more active oxygenating agent than bottle oxygen, which Vis Vgenerally understood Vto .be molecular oxygen, ,not-V only as produced inthe cell vbut ,also .for a substantial `length of time after it is drawn off from thecell. Y

V According torthis invention we therefore employ the oxygen generated by electrolysis withinthe cell,,outsideV of thecell by-,'brinlging itguickly into reacting .corviftact with .the solution Ycontaining y.the .mercaptides..before its activity has reverted :to that ofnbottleH oxygen.V

- his invention has, among. ther advantages, the 'following: p p v Y Y (l) A'highly eiheient .and effective electrolyticcell is maintained with a substantially constant electrolyte, such as caustic potash, Aby merely' addingwater toreplace that which is decomposed in the cell Vinto ,hydrogen and .oxygenwithout Aanyv contamination :or change V`vvwhich .takes place when oxidationrof the V,mercaptidhes is `going on within' the cell, as in thewprior art process de- -scribed, for example, in -Gaylor'fPatent No.. 2,654,106.

(2) The oxygengenerated in thefcellfis drawnfguiclrly into contact and Vreacts with -thefcspent caustic gironi' the .treatment 4of Vthe -gasoline which is `thereby effectively regenerated outside of the cell. he disuldesarewashed Aout Iof Lthe regenerated caustic jsolution by n aphtha in-the-usual'way. c

VIt has been discovered that thecaustic recovered-by .the use of this invention is somuch more `,eifectivein treating gasoline than .caustic regeneratedfbyfothermeans -that rkthe lead susceptibility of thegasoline is v,yeryisub- .-stantially increased.

YThe process ofV this invention -may be readily understood by reference to the `attached drawingsl in twhich:

iFig. .1 isV a ow diagram of a process embodying our invention-for treating sour gasoline withcausti .aridvv e011- `tinuously rregenerating the caustic -,With Yoxygen -`ldrawn Vdirectlyirom anelectrolytic cell. f

',Fig. 2 isaowdiagrfam of a process-:fordreatingwaste waters -in accordance with our invention Wherebylthey are V rendered suitable for discharge .into lakes. or yrivers withoutimpropercontamination;,and n Fig. 3 is a cross-sectional viewof .an .eductor .which ,isgsuitable-for use in' either of the processes illustrated inFigs.vl and 2.

Referring to Fig. 1 sour gasolineV4 to beitreated. is fin Vtroduced A`through line 1 into a packed tower f2`..where it is given van 'initial caustic treatmentifor Vr'e'111oving:.1;he hydrogen-sulfide (H28) and fromwhichitllowsithrough line 3 to the-treating tower 8. 'i

The sourgasoline enters'tower 2 near'the bottom and discharges .a't the top, a suitable treating "fluid, such as caustic soda, is ,supplied lthrough'linel14 and valve ,V5 into the .packed tower 2 near the top V.andimay bev drawn out'near :thel bottomthrough .Valve 6 ,and ldischarge Vline 7. .This operation lis operated primarily as Va `batch operation so far as-thecaustic wash-is concerned, foul caustic being withdrawn periodically, v*for example, once -a week and fresh caustic supplied from line 4-throughrvalve K5. The initially treated .gasoline -enters packed tower 8 near the bottom and leaves at the topn'throvugh line 9 from which it passesthrough a knock-,out drum "10 inthe usual manner and leaves ythrough line 11 vas ,treated product.

Patented Nov. 4, 195s A streamiof 'treating fluid, such as caustic soda, is supplied through line 12 and enters tower-8 at its upperY Y pump 15, which as above described, forces the caustic Y solution from' tank 14 through the eductor.YV The eductor requires a' high pressure at the nozzle'iwhich is suddenly released, as is Well known: "Moreover, the oxygenYwhich is kdrawn into theejector is intimately mixed with the caustic stream by reason of'thesecharacteristics Yof the eductor.

VThe mixing `is further augmented Aby theactiontotj the pump x15 which,l as shown, rapidly circulates the mixed solution and oxygen through-'theV circuit comprised ofthe pipe 24, valve 16, eductor'17and the'valve 1x8. The electrolytic cellcontains 'an electrolyte kwhich is well adapted to the continuous production of oxygen by electrolysis, suchYas for example, a caustic potash solution,- and the direct current electricity is supplied tothe cell by rectilier 22, which may be connected to an` ordinary source of AxC. electric energy. l Y Y AThe oxygen which isproduced in gaseous form on the faceYV of the cellplatesn is withdrawn through line 23Yand thepltime element between thegeneration of the oxygen and its entering` the circulating stream Yof spentV caustic is very short,l so that the oxygen, which is still very active as'contrastedV to lmolecular oxygen, has not'had an opportunity to lose itsactivity or even approach the activity of bottle orgmolecular oxygen.- Y

The caustic soda which has been used to treat the sour gasoline in packed tower 8 contains mercaptides and other sulfur compounds which have'bee'n removed from the gasoline, and when this spentcaustic solution is supplied With the oxygen from the electrolytic cell, the `mercaptides are converted into disuldes which are insoluble and continue in suspension in the regenerated caustic solution, which flows Vfrom Athe circuitthrough line 24 into regenerated caustic tank `25. Y Y

A pump 26 carries vthe regenerated caustic containing the disuldes into a disulde 'scrubber tank 27 containing naphtha, for example, and the regenerated caustic free from the disulfidesflows ,out from the bottom of the scrubber and returns through line 12to the top of the treating tower 8. ij. v Y

Other uids which require oxygen-fo'rY revivication may also be successfullytreated with oxygen, outside of the electrolytic cell where it is generated by means of our invention; anothersexample of such' fluidrbeing the spent acid catalyst from a sulfuric acid alkylation process. Such spent acid catalyst has the formula C4H9HSO4,

and when oxygen as generated in an electrolytic cell is v added to this fluid,V it results in the production of CO2 which escapes as a gas 'and H2O and H2804. The acid and water mixture is brought up to 98% concentrationby adding oleum H2SO4.SO3 in the usual manner.

Another embodiment of our-invention Vis illustrated in Fig. 2, to which reference is now made. Here oxygen as generated in an electrolytic'cell is utilized to `purify waste Waters from oil refineries, paper mills, or theflike. The treating of West Texas distillates results in a waste chemical solution composed of sodium .polysulfides having a formula Na2S4. This is produced by adding sulfur to sodium sulide as represented by the formula .Sodium polysulfide waste is very deficient in oxygen and 1s very detrlmental to any lake or Vriver waterand cannot safely be discharged without treatment. SuhYQCati ment may, however, be accomplished economically by theI Yuse of our invention. Y Y YY Y Y Y Y Y The waste process water enters the systemthroughrline: 35 and is forced by a pump 36 into a tank 37, from thencey it is recirculated through line 38 through eductor 39,Y pressure tank 4l) and is returned to the' tank 37. The recirculated etiuent flowing through the eductor pulls oxy-.IV

gen-gasr as generated in electrolytic cell 41 and flows; through line 42,V to the suction side of the eductor. Thel arrangement is such as to produce thorough mixing of the. oxygen with the waste process water.

'TheYcell may have any suitable electrolyte, such asf Y caustic potash and is supplied with directYcurrent by rectifierY 43, which in turn is connected'to an ordinary source of electric power as indicated at 44. Y

The oxygen in this case valso is Yutilized in gaseous form before it has lost its initial activity as compared' withVY bottle or molecular oxygen. Thus the time element "in- Y volved in the depreciation in activity of the oxygen as gen` erated inthe electrolytic cell is taken advantage of, ,so

that the oxygen eiciently Ycreates the desired'chemi'cal i change in the waste water. The formula whichwe 'believe represents the change in the particular'was'te solution abovediscussed is 4Na2S4-l-24O24Na'2s406, Ywhich is sodium tetrathionate, a harmless solution that may be safely discharged into lakes or rivers. i' In attempting to employ bottle or Ymolecular oxyge forrthe herein described oxidizing processes it hasl been demonstrated that the results are very meagerfunsatisfactory and -uneconomical inthe absence of a'catalyst, lwhereas the oxygen generated inrthe cell when used` quickly gives highly satisfactory and eifective oxidation and makes the processes commercially feasible.

According to a specific example of the use of our process, 1800 milliliters of spent treating solution having ,Y a mercaptan number of 531 milligrams per 100 milliliters has been regenerated by contacting oxygen as generated in an electrolytic cell in theV external system to a treating solution having a mercaptan number 'of 456,

in yive minutes by applying a current density of 15 amperes per 1A square foot, which is Vequivalent to 60 amperes per square foot anode area in thecell.

The eiciency of the process is the weight of mercaptan sulfur oxidized, times-.7100 divided by the theoretical weight of mercaptan sulfur based on 1.2 grams (see Perrys Chemical Engineering Handbook, 3rd edition,V

1950, page 1779) per ampere hour per square foot. Hence the percent oxidation of mercaptan sulfur to disuliide sulfur in the above example is equal to An example which is typicalvof the Vcommercial operation of the process of this invention is as follows:

Caustic treating and regeneration unit Pressure Distillate Y Caustic l(grams per liter) Y Y Y Current Mercaptan Sulfur, supplied percent by Weight Spent Regenerated to cell,

Y amperes In out His RsH Hts BSH i V.o2 .0034 0 `.soY Vo .16 9,000

Tests made to determine the activity of the oxygen pro'- from the cell reaches the caustic solution to be regenerated at the ejector in approximately 58 seconds, and with good mixing in both cases the percentage conversion with the oxygen from the electrolytic cell gives approximately twice the eiciency as bottle oxygen under the same conditions.

(3) Tests indicate that oxygen which is approximately 130 seconds old has lost approximately 20% of its effectiveness during the second minute of its life. The conversion eciencies of electrolytic oxygen in regenerating spent caustic solution range from 99.5%, with intimate mixing, to 26.4% with poor mixing. VBottle oxygen under the same mixing conditions and applied to the same caustic solution, was approximately one half as eiective as the electrolytic oxygen.

The eiciency of the process if carried on inside of the cell is much lower.

Su'cient Water will be added to the cell to make up not only for that which is decomposed but also for any net loss of moisture which escapes with the oxygen and hydrogen gases.

Commercial cells designed to operate at low pressure for the production of oxygen and hydrogen are entirely suitable for use in carrying out our invention, whereas the etciency of the treating operation is sacriced and the cell must be made to withstand relatively high pressure conditions at greatly increased cost if the spent treating uid ows through the cell and is oxidized therein in accordance with the prior art process. In fact, the maximum pressure obtained in a commercial electrolytic cell is too W for the best results.

In referring to oxygen as generated in an electrolytic cell, We mean the oxygen gas produced on the anode of an electrolytic cell, and We have discovered that the time element within which this oxygen fades in activity v to that of bottle or molecular oxygen is not instantaneous, as heretofore supposed, but is much longer and, while we now believe that it begins to age or to combine within about 2 minutes, its activity is substantially that of the newly generated oxygen for a suicient time to obtain caustic regenerationof high eiciency outside the cell where the oxygen is produced.

While we have described the invention as applied to diierent specific examples, these are intended to be illustrative only, and only such limitations should be imposed as appear in the appended claims.

This application is a continuation-impart of our application Serial No. 390,055, tiled November 3, 1953, now abandoned.

What we claim is:

1. The process of treating sour hydrocarbon oils which consists of pretreating the oil with a caustic wash to remove the hydrogen sulfide (HgS), washing the oil by a continuous countercurrent stream of caustic solution to remove the mercaptides, electrolytically generating oxygen, regenerating the spent caustic solution containing mercaptides by injecting into the stream of spent causticV solution the oxygen as generated Within a time element of 10 minutes and Without passing the caustic solution through the electrolytic cell.

2. 'I'he process of treating sour hydrocarbon oils which consists of washing the oil by a continuous countercurrent stream of caustic solution to remove the mercaptides, electrolytically generating oxygen, regenerating the spent caustic solution containing mercaptides by injecting into the stream of spent caustic solution the oxygen as generated within a time element of 2 minutes Without passing the caustic solution through the electrolytic cell Where the oxygen is produced.

3. The process for treating sour gasoline which consists of removing the hydrogen sulfide (H28) without removing the mercaptides, washing the gasoline with a caustic solution to remove the mercaptides, electrolytically generating oxygen independently of said caustic solution and regenerating the spent caustic solution by immediately mixing the oxygen outside of the electric cell where the oxygen is produced Within the time element during which the oxygen retains a substantial part of its initial activity as contrasted to molecular Voxygen with the spent caustic solution to oxidize the mercaptides to form disulfides. i

4. The process for treating sour gasoline which consists of removing the hydrogen sulde (HZS) Without removing the mercaptides, Washing the gasoline with a. caustic solution to remove the mercaptides and electrolytically generating oxygen, regenerating the spent'caustic solution by immediately mixing the oxygen outside of the electric cell Where the oxygen is produced before theV activity of the oxygen has had time to depreciate to that of molecular oxygen with the spent caustic solution to oxidize the mercaptides to form disuldes in the absenceof a catalyst. i

5. The process of regenerating spent caustic solution containing mercaptides which consists of electrolytically decomposing water in an electrolyte solution independent of the caustic solution to form active oxygen, Withdrawing the active oxygen from the electrolytic cell and immediately introducing it outside of the cell into and intimately mixing it with the spent caustic solution While the activity of the oxygen is greaterthan that of molecular oxygen, to form disulides.

6. The process of regenerating spent caustic solution containing mercaptides which consists of electrolytically decomposing Water in an electrolyte solution to form active oxygen, WithdraWingthe active oxygen from the electrolytic cell and immediately introducing it into the spent caustic solution before the active oxygen has lost its activity as compared to molecular oxygen.V

7. The process of claim 6 in which vthe electrolyte is chemically dissimilar from the spent caustic solution.

8. The process of claim 6 in which the caustic solution containing mercaptides is a caustic soda solution and the electrolyte is a caustic potash solution.

References Cited in the le of this patent UNITED STATES PATENTS 1,139,778 Landreth May 18, 1915 1,828,872 Marsh Oct. 27, 1931 2,130,789 Campbell Sept. 20, 1938 2,270,376 Ladd Jan. 20, 1942 2,470,073 Low May 10, 1949 2,654,706 Y Gaylor -v.--ff--fa-f.- Ot- 6. 19.5.3 

1. THE PROCESS OF TREATING SOUR HYDROCARBON OILS WHICH CONSISTS OF PRETREATING THE OIL WITH A CAUSTIC WASH TO REMOVE THE HYDROGEN SULFIDE (H2S), WASHING THE OIL BY A CONTINUOUS COUNTERCURRENT STREAM OF CAUSTIC SOLUTION TO REMOVE THE MERCAPTIDES, ELECTROLYTICALLY GENERATING OXYGEN, REGENERATING THE SPENT CAUSTIC SOLUTION CONTAINING MERCAPTIDES BY INJECTING INTO THE STREAM OF SPENT CAUSTIC SOLUTION THE OXYGEN AS GENERATED WITHIN A TIME ELEMENT OF 10 MINUTES AND WITHOUT PASSING THE CAUSTIC SOLUTION THROUGH THE ELECTROLYTIC CELL. 